Solvent‐Free Approach to 3,4‐Dihydropyrimidin‐2(1H)‐(thio)ones: Biginelli Reaction Catalyzed by a Wells–Dawson Reusable Heteropolyacid

Sulfamic acid pyromellitic diamide-functionalized MCM-41 as a multifunctional hybrid catalyst for melting-assisted solvent-free synthesis of bioactive 3,4-dihydropyrimidin-2-(1H)-ones

This study introduces a practical approach to fabricate a novel hybrid acidic catalyst, namely sulfamic acid pyromellitic diamide-functionalized MCM-41 (MCM-41-APS-PMDA-NHSO₃H). Various techniques such as FTIR, TGA, XRD, BET, FESEM, and EDX were used to confirm its structural characteristics. The efficiency of the new MCM-41-APS-PMDA-NHSO₃H organosilica nanomaterials, as a heterogenous nanocatalyst, was examined in the synthesis of biologically active 3,4-dihydropyrimidin-2-(1H)-one derivatives under solvent-free conditions. It was found that the nanoporous MCM-41-APS-PMDA-NHSO₃H, demonstrating acidic nature and high surface area, can activate all the Biginelli reaction components to afford desired 3,4-dihydropyrimidin-2-(1H)-ones under solvent-free conditions in short reaction time. Furthermore, easy and quick isolation of the new introduced hybrid organosilica from the reaction mixture as well as its reusability with negligible loss of activity in at least five consecutive runs are another advantages of this green protocol.

Biginelli Reaction: Polymer Supported Catalytic Approaches

The Biginelli product, dihydropyrimidinone (DHPM) core, and its derivatives are of immense biological importance. There are several methods reported as modifications to the original Biginelli reaction. Among them, many involve the use of different catalysts. Also, among the advancements that have been made to the Biginelli reaction, improvements in product yields, less hazardous reaction conditions, and simplified isolation of products from the reaction predominate. Recently, solid-phase synthetic protocols have attracted the research community for improved yields, simplified product purification, recyclability of the solid support, which forms a special economic approach for Biginelli reaction. The present Review highlights the role of polymer-supported catalysts in Biginelli reaction, which may involve organic, inorganic, or hybrid polymers as support for catalysts. A few of the schemes involve magnetically recoverable catalysts where work up provides green approach relative to traditional methods. Some research groups used polymer-catalyst nanocomposites and polymer-supported ionic liquids as catalyst. Solvent-free, an ultrasound or microwave-assisted Biginelli reactions with polymer-supported catalysts are also reported.

Nebivolol nanoparticles: a first catalytic use in Biginelli and Biginelli-like reactions

Herein, we report the catalytic activity of nebivolol nanoparticles a novel organocatalyst for the synthesis of DHPMs and DHPM-5-carboxamides. The nanoparticles are confirmed by DSC, TEM, AFM, and IR spectroscopy. The catalyst can be readily recovered and reused for the next four runs without any significant impact on the yields of the products. The products are fully characterized by FTIR, 1H NMR, 13C NMR, and distortionless enhanced polarization transfer (DEPT) NMR. The methodology adopted here offers several advantages such as solvent-free reaction, low loading of catalyst, short reaction times, and quantifiable yields.

Sulfated polyborate: a new and eco-friendly catalyst for one-pot multi-component synthesis of 3,4-dihydropyrimidin-2(1H)-ones/thiones via Biginelli reaction

A highly efficient and improved synthetic methodology for the preparation of 3,4-dihydropyrimidin-2(1H)-one derivatives in good to excellent yield via Biginelli reaction of β-ketoesters/β-diketone, urea/thiourea and various aldehydes using new, efficient and recyclable sulfated polyborate catalyst under the solvent-free condition is reported.